This invention is directed to a fire retardant material which utilizes a permeable mass of glass permeated with the unexpanded form of perlite. Upon exposure to combustion temperatures the heat expandable material expands followed by reaction of this material with the glass to form a ceramic.
It has been the goal of certain industries to produce structural materials such as roofing compositions and insulation which are capable of retarding the spread of flame in case of catastrophic fire in a building. To this end, certain specifications have been set up as guidelines in evaluating these materials for their flame retardant properties. Underwriters' Laboratory tests set forth specific parameters in tests of materials for their flame retardant abilities. UL test 790 includes Fire Brand tests as part of these parameters. The Fire Brand tests are rated such as Fire Brand A, Fire Brand B and Fire Brand C. The criteria of the A and B tests are very stringent and most products fail to meet them.
Certain inorganic compositions which themselves are not combustible have been incorporated into both roofing materials and insulation. Use of these materials, however, is governed by many factors. They, of course, must be available in large quantities and at an economical price. By their very nature, however, they tend to be extremely dense and thus impractical to use by themselves because of the structures needed to support their weight. Further, solid bodies of these inorganic materials tend to be extremely brittle. Although they have considerable compression strength, their sheer strength is extremely poor. For these reasons, if these materials are used it has been found necessary to normally incorporate them into matrices of other materials.
The above noted fire resistant materials include materials such as clays, silicas, glasses and minerals such as asbestos, expanded perlite and expanded vermiculite. Asbestos is not suited for most uses because of the health hazard associated with fine fibers within the lungs. Clays and the like are so extremely dense that their use is limited to certain installations, such as tile roofs, floor tiles and the like. Except for brick walls, the use of clays cannot be extended to walls. Expanded perlite and vermiculite have no structural strength when used neat, and thus cannot be used without other supporting materials.
Expanded perlite and vermiculite, however, have been found to be useful as fillers in insulation and to reduce the density of certain aggregates. In this regard other structural components are used to impart structural strength to the insulation or aggregate and the expanded perlite or vermiculite is added to this to form dead areas within the matrix of the structural material.
When the expanded perlite or vermiculite is used as a filler in insulation they impart very good fire retardant properties to the material. However, the matrix material which is used to support them in the past has either been extremely dense inorganic composition or has been a material which is susceptible to combustion, such as organic resins and the like. Examples of use of expanded perlite and vermiculite within matrices are found in U.S. Pat. Nos. 3,987,018; 4,011,195; 2,634,208 and 2,884,380. In these notes U.S. patents, which use an expanded composition in an organic matrix, the products described therein will only be useful at temperatures below that of the combustion point of the matrix material.
In a fire, the presence of an insulating material will help slow the heat spread from one area to an adjoining area. In addition to heat spread, it is also desirable to inhibit gas movement to seal off the fire. Thus, in addition to serving as an insulating material, materials which are effectively impenetrable to gas movement assist in preventing flame spread by inhibiting oxygen availability to the source of the combustion. Those insulating materials which are either porous or which have a combustible matrix are therefore of little utility in inhibiting movement of oxygen to the source of the flame.
In view of the above discussion it is evident that there exists a need for materials which are capable of serving as insulators and flame spread preventers or inhibitors. Certain presently used construction materials, such as concrete or metals, can serve to meet this need. However, in certain structures their use is precluded by either their weight, their cost, or architectural considerations. In these types of structures the need for efficient fire retardant materials has not yet been satisfied.